Re: [HACKERS] [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

On Thu, Nov 9, 2017 at 4:17 PM, Andres Freund <andres@anarazel.de> wrote:
>> Actually, on second thought, I take that back -- I don't think that
>> REINDEXing will even finish once a HOT chain is broken by the bug.
>> IndexBuildHeapScan() actually does quite a good job of making sure
>> that HOT chains are sane, which is how the enhanced amcheck notices
>> the bug here in practice.
>
> I think that's too optimistic.

Why? Because the "find the TID of the root" logic in
IndexBuildHeapScan()/heap_get_root_tuples() won't reliably find the
actual root (it might be some other HOT chain root following TID
recycling by VACUUM)?

Assuming that's what you meant: I would have thought that the
xmin/xmax matching within heap_get_root_tuples() makes the sanity
checking fairly reliable in practice.

-- 
Peter Geoghegan


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